WASHINGTON — President Trump on Wednesday warned again about the dangers of undocumented immigrants, signaling no plans to temper his rhetoric even as he prepares to unveil a broad proposal aimed at balancing public perception of his administration’s hard-line agenda.

Trump is scheduled to use a Rose Garden speech on Thursday to throw his support behind a plan developed by his son-in-law and White House adviser, Jared Kushner, to move US immigration toward a ‘‘merit-based system’’ that prioritizes high-skilled workers over those with family already in the country. Several Republican senators are expected to attend, officials said.

The proposal, previewed by Kushner and other Trump aides in private briefings on Capitol Hill over the past two weeks, already is facing skepticism from lawmakers in both parties, and there appears to be no clear path toward advancing the plan through Congress.

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But White House aides emphasized that Trump is enthusiastically on board with an effort to demonstrate that he endorses legal immigration to help American companies even as he has railed against other groups, including immigrant families seeking asylum and refugees.

‘‘This is his proposal,’’ said a senior administration official who spoke on the condition of anonymity. ‘‘He’s been intimately involved in crafting it. We've shown him kind of where some of the criticism might come from on the right, and his response is, ‘I'm happy to talk to them and I'll convince them of why this is the right thing.' ’’

The rollout presents another test of Trump’s willingness to stump for a plan that could face opposition from border hawks and his ability to forge bipartisan support at a time when he has inflamed Democrats over unilateral immigration actions, including declaring a national emergency to pay for a border wall.

In past immigration debates, including the Senate’s deliberation over four immigration bills in early 2018, Trump floated support for more liberal immigration positions only to quickly revert to his hard-line stance in the wake of criticism from conservatives.

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That has led to skepticism over just how far Trump will go to build support for a plan that White House aides said does not curtail the overall number of immigration green cards, a major goal of many border hawks.

In a memorial service for slain law enforcement officers Wednesday, Trump showed no signs that he would shift his tone about immigrants to build more moderate support. The president highlighted the case of Corporal Ronil Singh, a police officer who authorities said was killed by an unauthorized immigrant from Mexico during a traffic stop in December.

Trump called the perpetrator a ‘‘vicious killer’’ who could have been kept out of the country by a border wall or ‘‘whatever the hell it takes.’’

‘‘People are trying to come into our country because our country’s doing well,’’ Trump said. ‘‘They can’t come in like this killer came in.’’

Congress has not passed a major immigration bill in three decades, and efforts at comprehensive changes failed under Presidents George W. Bush and Barack Obama, both of whom emphasized the need to balance efforts to beef up enforcement with the need to expand legal pathways into the United States.

Trump’s administration has sharply curtailed the number of refugees in the country and has attempted repeatedly to strip asylum rights for a record number of Central American families that have crossed the US border with Mexico.

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The United States issues more than 1 million green cards each year, granting foreigners legal permanent residency, of which about 140,000 are based on employment and the rest on family ties, refugees status and a diversity lottery.

The new White House plan would distribute more than half of the green cards to immigrants under a point system in which applicants are ranked on such criteria as professional skills, education levels, age, and English ability, White House aides said.

Another criterion, aides said, would be ‘‘patriotic assimilation,’’ a concept that would favor immigrants who had shown an active interest in incorporating the nation’s culture and way of life. One administration official offered an example in which green-card applicants would be required to pass an exam based on a reading of George Washington’s farewell address or Thomas Jefferson’s letter to the Danbury Baptist Association.

The White House proposal also would seek to address the mounting border crisis, where the surge of families have overwhelmed the US immigration system. And aides said the plan would call for modernizing legal ports of entry to help prevent the flow of illicit drugs and human trafficking, while also proposing changes to make US asylum laws stricter — something Democrats have resisted.

But the White House officials said the plan does not address the fate of up to 2 million younger immigrants, known as ‘‘Dreamers,’’ who have lived in the country illegally since they were brought in as children.

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Trump met with a dozen GOP senators at the White House last week, and several emerged to characterized the plan as a ‘‘political document’’ that Republicans can rally around as Democrats seek to demonize the president on immigration ahead of the 2020 election.

The White House proposal is ‘‘not designed to become law,’’ Senator Lindsey Graham, Republican of South Carolina and a Trump ally, said Wednesday.

Senate minority leader Charles Schumer, Democrat of New York, said the White House has ‘‘not even talked to Democrats’’ about the plan and expressed doubt that it would win support from his party.